Resist composition and patterning process

ABSTRACT

A resist composition contains a polymer-bound acid generator, specifically a polymer comprising recurring units derived from a sulfonium or iodonium salt having a polymerizable unsaturated bond and containing iodine in the linker between the polymerizable unsaturated bond and a fluorosulfonic acid. The resist composition offers a high sensitivity and improved CDU independent of whether it is of positive or negative tone.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2017-100594 filed in Japan on May 22,2017, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition and a patterning processusing the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, EUV lithography ofwavelength 13.5 nm, and double patterning version of the ArFlithography, on which active research efforts have been made.

As the pattern feature size is reduced, approaching to the diffractionlimit of light, light contrast lowers. In the case of positive resistfilm, a lowering of light contrast leads to reductions of resolution andfocus margin of hole and trench patterns.

As the pattern feature size is reduced, the edge roughness (LWR) of linepatterns and the critical dimension uniformity (CDU) of hole patternsare regarded significant. It is pointed out that these factors areaffected by the segregation or agglomeration of a base polymer and acidgenerator and the diffusion of generated acid. There is a tendency thatas the resist film becomes thinner, LWR becomes greater. A filmthickness reduction to comply with the progress of size reduction causesa degradation of LWR, which becomes a serious problem.

The EUV lithography resist must meet high sensitivity, high resolutionand low LWR at the same time. As the acid diffusion distance is reduced,LWR is reduced, but sensitivity becomes lower. For example, as the PEBtemperature is lowered, the outcome is a reduced LWR, but a lowersensitivity. As the amount of quencher added is increased, the outcomeis a reduced LWR, but a lower sensitivity. It is necessary to overcomethe tradeoff relation between sensitivity and LWR

Patent Document 1 discloses a resist compound comprising recurring unitsderived from an onium salt of a polymerizable unsaturatedbond-containing sulfonic acid. The so-called polymer-bound acidgenerator is capable of generating a polymer type sulfonic acid uponexposure and characterized by a very short distance of acid diffusion.Sensitivity may be enhanced by increasing a proportion of the acidgenerator. In the case of addition type acid generators, as the amountof acid generator added is increased, a higher sensitivity isachievable, but the acid diffusion distance is also increased. Since theacid diffusion is non-uniform, increased acid diffusion leads todegraded LWR and CDU. With respect to a balance of sensitivity, LWR andCDU, the polymer-bound acid generator has a high capability.

CITATION LIST

Patent Document 1: JP 4425776

DISCLOSURE OF INVENTION

In the field of acid-catalyzed chemically amplified resist materials, itis desired to have a resist material having a higher sensitivity,improved LWR of line patterns, and improved CDU of hole patterns.

An object of the invention is to provide a resist composition whichexhibits a high sensitivity and a reduced LWR or improved CDU,independent of whether it is of positive tone or negative tone; and apattern forming process using the same.

The inventors have found that using a polymer comprising recurring unitsderived from a sulfonium or iodonium salt having a polymerizableunsaturated bond and containing a iodine atom in the linker between thepolymerizable unsaturated bond and a fluorosulfonic acid, as thepolymer-bound acid generator, a resist material having a highsensitivity, reduced LWR, improved CDU, high contrast, improvedresolution, and wide process margin is obtainable.

In one aspect, the invention provides a resist composition comprising apolymer comprising recurring units having the formula (a1) or (a2).

Herein R^(A) is hydrogen or methyl; X¹ is a single bond or ester group;X² is a C₁-C₁₂ straight, branched or cyclic alkylene group or C₆-C₁₀arylene group, any methylene moiety in the alkylene group may besubstituted by an ether moiety, ester moiety or lactone ring-containingmoiety, at least one hydrogen in the group X² is substituted by iodine;X³ is a single bond, ether group, ester group or C₁-C₁₂ straight,branched or cyclic alkylene group, any methylene moiety in the alkylenegroup may be substituted by an ether or ester moiety; Rf¹ to Rf⁴ areeach independently hydrogen, fluorine or trifluoromethyl, at least oneof Rf¹ to Rf⁴ is fluorine or trifluoromethyl, Rf¹ and Rf² may bondtogether to form a carbonyl group; R¹ to Rf⁴ are each independently aC₁-C₁₂ straight, branched or cyclic alkyl group, C₂-C₁₂ straight,branched or cyclic alkenyl group, C₂-C₁₂ straight, branched or cyclicalkynyl group, C₆-C₂₀ aryl group, C₁-C₂ aralkyl group, or C₇-C₁₂aryloxyalkyl group, in which at least one hydrogen may be substituted byhydroxyl, carboxyl, halogen, oxo, cyano, amide, nitro, sultone, sulfoneor sulfonium salt-containing moiety, and in which any methylene moietymay be substituted by an ether, ester, carbonyl, carbonate or sulfonatemoiety, and R¹ and R² may bond together to form a ring with the sulfuratom to which they are attached.

Preferably the recurring units having formulae (a1) and (a2) arerepresented by the formulae (a1-1) and (a2-1), respectively.

Herein R^(A), R¹ to R⁵, Rf⁴ to Rf⁴, and X¹ are as defined above; R⁶ is aC₁-C₄ straight, branched or cyclic alkyl group, halogen atom exclusiveof iodine, hydroxyl group. C₁-C₄ straight, branched or cyclic alkoxygroup, or C₂-C₅ straight, branched or cyclic alkoxycarbonyl group, m isan integer of 1 to 4, and n is an integer of 0 to 3.

The resist composition may further comprise an organic solvent.

In a preferred embodiment, the polymer further comprises recurring unitshaving to the formula (b1) or (b2).

Herein R^(A) is independently hydrogen or methyl; Y¹ is a single bond,phenylene group, naphthylene group, or a C₁-C₁₂ linking group containingan ester moiety and/or lactone ring; Y² is a single bond or ester group;R¹¹ and R¹² are each independently an acid labile group; R¹³ is halogen,trifluoromethyl, cyano, C₁-C₆ straight, branched or cyclic alkyl oralkoxy group, or C₂-C₇ straight, branched or cyclic acyl, acyloxy oralkoxycarbonyl group; R¹⁴ is a single bond or C₁-C₆ straight or branchedalkylene group in which at least one carbon atom may be substituted byan ether or ester moiety, p is 1 or 2, and q is an integer of 0 to 4.

The resist composition may further comprise a dissolution inhibitor, theresist composition being a chemically amplified positive tone resistcomposition.

In one embodiment, the polymer is free of an acid labile group. Theresist composition may further comprise a crosslinker, the resistcomposition being a chemically amplified negative tone resistcomposition.

The resist composition may further comprise a surfactant.

In another aspect, the invention provides a process for forming apattern comprising the steps of applying the resist composition definedabove onto a substrate, baking to form a resist film, exposing theresist film to high-energy radiation, and developing the exposed film ina developer.

In a preferred embodiment, the high-energy radiation is ArF excimerlaser radiation of wavelength 193 nm, KrF excimer laser radiation ofwavelength 248 nm, EB or EUV of wavelength 3 to 15 nm.

Advantageous Effects of Invention

A resist material containing a polymer comprising recurring unitsderived from a sulfonium or iodonium salt having a polymerizableunsaturated bond and containing iodine in the linker between thepolymerizable unsaturated bond and a fluorosulfonic acid has theadvantage of reduced acid diffusion because of the high atomic weight ofiodine. This prevents resolution from declining due to blur by aciddiffusion and enables to reduce LWR and improve CDU. Since iodine ishighly absorptive to EUV of wavelength 13.5 nm, it generates secondaryelectrons during exposure, contributing to a higher sensitivity. Thus aresist material having a high sensitivity, low LWR and improved CDU maybe designed.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(C_(n)-C_(m)) means a group containing from n to m carbon atoms pergroup. As used herein, the term “iodized” or “fluorinated” indicatesthat a compound contains iodine or fluorine. Me stands for methyl and Acfor acetyl.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

LWR: line width roughness

CDU: critical dimension uniformity

Resist Composition

The resist composition of the invention is defined as comprising apolymer-bound acid generator, specifically a polymer comprisingrecurring units derived from a sulfonium or iodonium salt having apolymerizable unsaturated bond and containing a iodine atom in thelinker between the polymerizable unsaturated bond and a fluorosulfonicacid. In the resist composition, another acid generator capable ofgenerating a sulfonic acid (different from the fluorosulfonic acid),imide acid or methide acid may be separately added.

When a resist composition containing the polymer-bound acid generator inadmixture with a sulfonium salt capable of generating weaker acid suchas sulfonic acid or carboxylic acid is exposed to radiation, afluorosulfonic acid polymer containing iodine in the linker and weakersulfonic acid or carboxylic acid generate. Since the acid generator isnot entirely decomposed, the undecomposed sulfonium salt is presentnearby. When the polymeric fluorosulfonic acid containing iodine in thelinker co-exists with the sulfonium salt of weaker sulfonic acid orcarboxylic acid, an ion exchange takes place between the polymericfluorosulfonic acid containing iodine in the linker and the sulfoniumsalt of weaker sulfonic acid or carboxylic acid, whereby a sulfonium oriodonium salt of polymeric fluorosulfonic acid containing iodine in thelinker is created and the weaker sulfonic acid or carboxylic acid isreleased. This is because the salt of polymeric fluorosulfonic acidcontaining iodine in the linker having a high acid strength is morestable. In contrast, when a sulfonium salt of polymeric fluorosulfonicacid containing iodine in the linker co-exists with a weaker sulfonicacid or carboxylic acid, no ion exchange takes place. The ion exchangereaction according to the acid strength series occurs not only withsulfonium salts, but also similarly with iodonium salts. When combinedwith an acid generator for fluorosulfonic acid, a sulfonium or iodoniumsalt of weak acid functions as a quencher. Since iodine is highlyabsorptive to EUV of wavelength 13.5 nm, it generates secondaryelectrons upon EUV exposure. The energy of secondary electrons istransferred to the acid generator to promote its decomposition,contributing to a higher sensitivity. The polymer-bound acid generatoris effective for achieving low acid diffusion and high sensitivity.

For the LWR improving purpose, it is effective to prevent a polymerand/or acid generator from agglomeration. Effective means for preventingagglomeration of a polymer is by reducing the difference betweenhydrophobic and hydrophilic properties or by lowering the glasstransition temperature (Tg) or molecular weight thereof. Specifically,it is effective to reduce the polarity difference between a hydrophobicacid labile group and a hydrophilic adhesive group or to lower the Tg byusing a compact adhesive group like monocyclic lactone. One effectivemeans for preventing agglomeration of an acid generator is byintroducing a substituent into the triphenylsulfonium cation. Inparticular, with respect to a methacrylate polymer containing analicyclic protective group and a lactone adhesive group for ArFlithography, a triphenylsulfonium composed solely of aromatic groups hasa heterogeneous structure and low compatibility. As the substituent tobe introduced into triphenylsulfonium, an alicyclic group or lactonesimilar to those used in the base polymer is regarded adequate. Whenlactone is introduced in a sulfonium salt which is hydrophilic, theresulting sulfonium salt becomes too hydrophilic and thus lesscompatible with a polymer, with a likelihood that the sulfonium saltwill agglomerate. When a hydrophobic alkyl group is introduced, thesulfonium salt may be uniformly dispersed within the resist film. WO2011/048919 discloses the technique for improving LWR by introducing analkyl group into a sulfonium salt capable of generating an α-fluorinatedsulfone imide acid.

The polymer-bound acid generator used herein is less diffusive becausethe anion moiety is bound to the polymer backbone and iodine having alarge atomic weight is introduced in the anion moiety, and higher inacid generation efficiency because iodine is highly absorptive. Sincethe acid generator is mixed with monomers prior to polymerization, theacid generator is uniformly dispersed in the polymer. These lead toimprovements in LWR and CDU.

The polymer-bound acid generator exerts a LWR or CDU improving effect,which may stand good either in positive and negative tone patternformation by alkaline development or in negative tone pattern formationby organic solvent development.

Polymer-Bound Acid Generator

The polymer-bound acid generator used herein is a polymer comprisingrecurring units derived from a sulfonium or iodonium salt having apolymerizable unsaturated bond and containing a iodine atom in thelinker between the polymerizable unsaturated bond and a fluorosulfonicacid and specifically, a polymer comprising recurring units having theformula (a1) or (a2). It is noted that recurring units having theformula (a1) or (a2) are simply referred to as recurring units (a1) or(a2), hereinafter.

Herein R^(A) is hydrogen or methyl. X¹ is a single bond or ester group.X² is a C₁-C₁₂ straight, branched or cyclic alkylene group or C₆-C₁₀arylene group, any methylene moiety in the alkylene group may besubstituted by an ether moiety, ester moiety or lactone ring-containingmoiety, and at least one hydrogen in the group X² is substituted byiodine. X³ is a single bond, ether group, ester group or C₁-C₁₂straight, branched or cyclic alkylene group, any methylene moiety in thealkylene group may be substituted by an ether or ester moiety. Rf¹ toRf¹ are each independently hydrogen, fluorine or trifluoromethyl atleast one of Rf¹ to Rf⁴ is fluorine or trifluoromethyl, and Rf¹ and Rf²may bond together to form a carbonyl group. R¹ to R⁵ are eachindependently a C₁-C₁₂ straight, branched or cyclic alkyl group, C₂-C₁₂straight, branched or cyclic alkenyl group, C₂-C₁₂ straight, branched orcyclic alkynyl group, C₆-C₂₀ aryl group, C₇-C₁₂ aralkyl group, or C₇-C₁₂aryloxyalkyl group, in which at least one hydrogen (one or more or evenall hydrogen atoms) may be substituted by hydroxyl, carboxyl, halogen,oxo, cyano, amide, nitro, sultone, sulfone or sulfonium salt-containingmoiety, and in which any methylene moiety may be substituted by anether, ester, carbonyl, carbonate or sulfonate moiety. Also, R¹ and R²may bond together to form a ring with the sulfur atom to which they areattached.

Preferably, the recurring units (a1) and (a2) are represented by theformulae (a1-1) and (a2-1), respectively.

Herein R^(A), R¹ to R⁵, Rf¹ to Rf⁴, and X¹ are as defined above. R⁶ is aC₁-C₄ straight, branched or cyclic alkyl group, halogen atom exclusiveof iodine, hydroxyl group, C₁-C₄ straight, branched or cyclic alkoxygroup, or C₂-C₅ straight, branched or cyclic alkoxycarbonyl group, m isan integer of 1 to 4, and n is an integer of 0 to 3.

Examples of the anion moiety in the monomer from which recurring units(a1) or (a2) are derived are given below, but not limited thereto.

Examples of the cation moiety in recurring unit (a1) are given below,but not limited thereto.

Examples of the cation moiety in recurring unit (a2) are given below,but not limited thereto.

The monomer from which recurring units (a1) or (a2) are derived may besynthesized, for example, by the same method as the synthesis of asulfonium salt having a polymerizable anion described in U.S. Pat. No.8,057,985 (JP 5201363).

The polymer-bound acid generator can also function as a base polymer. Inthis regard, where the resist composition is a chemically amplifiedpositive tone resist composition, the polymer-bound acid generator is apolymer further comprising recurring units containing an acid labilegroup, preferably recurring units having the formula (b1) or recurringunits having the formula (b2). These units are simply referred to asrecurring units (b1) and (b2).

Herein R^(A) is each independently hydrogen or methyl. Y¹ is a singlebond, phenylene group or naphthylene group, or C₁-C₁₂ linking groupcontaining ester moiety and/or lactone ring. Y² is a single bond orester group. R¹¹ and R¹² are each independently an acid labile group.R¹³ is halogen, trifluoromethyl, cyano, a C₁-C₆ straight, branched orcyclic alkyl or alkoxy group, or a C₂-C₇ straight, branched or cyclicacyl, acyloxy or alkoxycarbonyl group. R¹⁴ is a single bond or C₁-C₆straight or branched alkylene group in which one or more carbon atomsmay be substituted by an ether or ester moiety, p is 1 or 2, and q is aninteger of 0 to 4.

Examples of the recurring units (b1) are shown below, but not limitedthereto. R^(A) and R¹¹ are as defined above.

Examples of the recurring units (b2) are shown below, but not limitedthereto. R^(A) and R¹² are as defined above.

The acid labile groups represented by R¹¹ and R¹² in formulae (b1) and(b2) may be selected from a variety of such groups, for example, thosegroups described in JP-A 2013-080033 (U.S. Pat. No. 8,574,817) and JP-A2013-083821 (U.S. Pat. No. 8,846,303).

Typical of the acid labile group are groups of the following formulae(AL-1) to (AL-3).

In formulae (AL-1) and (AL-2), R²¹ and R²⁴ are each independently amonovalent hydrocarbon group of 1 to 40 carbon atoms, preferably 1 to 20carbon atoms, typically straight, branched or cyclic alkyl, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. R²²and R²³ are each independently hydrogen or a monovalent hydrocarbongroup of 1 to 20 carbon atoms, typically straight, branched or cyclicalkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. Any two of R²², R²³ and R²⁴ may bond together to form aring, typically alicyclic, with the carbon atom or carbon and oxygenatoms to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms. The subscript k is an integer of0 to 10, especially 1 to 5.

In formula (AL-3), R²⁵, R²⁶ and R²⁷ are each independently a monovalenthydrocarbon group of 1 to 20 carbon atoms, typically straight, branchedor cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. Any two of R²⁵, R²⁶ and R²⁷ may bond together toform a ring, typically alicyclic, with the carbon atom to which they areattached, the ring containing 3 to 20 carbon atoms, preferably 4 to 16carbon atoms.

When the polymer-bound acid generator also functions as a base polymer,the polymer may further comprise recurring units (c) having a phenolichydroxyl group as an adhesive group. Examples of suitable monomers fromwhich recurring units (c) are derived are given below, but not limitedthereto. Herein R^(A) is as defined above.

When the polymer-bound acid generator also functions as a base polymer,the polymer may further comprise recurring units (d) having anotheradhesive group selected from hydroxyl (other than the foregoing phenolichydroxyl), carboxyl, lactone ring, ether, ester, carbonyl and cyanogroups. Examples of suitable monomers from which recurring to units (d)are derived are given below, but not limited thereto. Herein R^(A) is asdefined above.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

When the polymer-bound acid generator also functions as a base polymer,the polymer may further comprise recurring units (e) derived fromindene, benzofuran, benzothiophene, acenaphthylene, chromone, coumarin,and norbornadiene, or derivatives thereof. Suitable monomers areexemplified below.

When the polymer-bound acid generator also functions as a base polymer,the polymer may further comprise recurring units (f) derived fromindane, vinylpyridine or vinylcarbazole.

In a further embodiment, the polymer-bound acid generator may furthercomprise recurring units (g) derived from an onium salt having apolymerizable unsaturated bond other than the recurring units (a1) and(a2). Typical recurring units (g) are described, for example, in U.S.Pat. No. 9,810,983 (JP-A 2017-008181, paragraph [0060]).

The base polymer for formulating the positive resist compositioncomprises recurring units (a1) and/or (a2) and recurring units (b1)and/or (b2) having an acid labile group as essential components andadditional recurring units (c), (d), (e), (f) and (g) as optionalcomponents. A fraction of units (a1), (a2), (b1), (b2), (c), (d), (e),(f), and (g) is: preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0, 0≤b1<1.0,0≤b2<1.0, 0<b1+b2<1.0, 0≤c≤0.9, 0≤d≤0.9, 0≤e≤0.8, 0<f<0.8, and 0≤g≤0.4;more preferably 0≤a1≤0.7, 0≤a2≤0.7, 0.02≤a1+a2≤0.7, 0≤b1≤0.9, 0≤b2≤0.9,0.1≤b1+b2≤0.9, 0≤c≤0.8, 0≤d≤0.8, 0≤e≤0.7, 0≤f≤0.7, and 0≤g≤0.3; and evenmore preferably 0≤a1≤0.5, 0≤a2≤0.5, 0.03≤a1+a2≤0.5, 0≤b1≤0.8, 0≤b2≤0.8,0.1≤b1+b2<0.8, 0≤c≤0.7, 0≤d≤0.7, 0≤e≤0.6, 0≤f≤0.6, and 0≤g≤0.2. Notably,a1+a2+b1+b2+c+d+e+f+g=1.0.

For the base polymer for formulating the negative resist composition, anacid labile group is not necessarily essential. The base polymercomprises recurring units (a1) and/or (a2) as essential component, andadditional recurring units (c), (d), (e), (f) and (g) as optionalcomponents. A fraction of these units is: preferably 0≤a1<1.0, 0≤a2<1.0,0<a1+a2<1.0, 0≤c<1.0, 00≤d≤0.9, 0≤e≤0.8, 0≤f≤0.8, and 0≤g≤0.4; morepreferably 0≤a1≤0.7, 0≤a2≤0.7, 0.02≤a1+a2≤0.7, 0.2≤c<1.0, 0≤d≤0.8,0≤e≤0.7, 0≤f≤0.7, and 0<g≤0.3; and even more preferably 0≤a1≤0.5,0≤a2≤0.5, 0.03≤a1+a2≤0.5, 0.3≤c<1.0, 0≤d≤0.75, 0≤e≤0.6, 0≤f≤0.6, and0≤g≤0.2. Notably, a1+a2+c+d+e+f+g=1.0.

The polymer-bound acid generator may be synthesized by any desiredmethods, for example, by dissolving suitable monomers selected from themonomers corresponding to the foregoing recurring units in an organicsolvent, adding a radical polymerization initiator thereto, and heatingto conduct polymerization. Examples of the organic solvent which can beused for polymerization include toluene, benzene, tetrahydrofuran (THF),diethyl ether, and dioxane. Examples of the polymerization initiatorused herein include 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis, for thereby converting the relevantunits to hydroxystyrene or hydroxyvinylnaphthalene units. For alkalinehydrolysis, a base such as aqueous ammonia or triethylamine may be used.Preferably the reaction temperature is −20° C. to 100° C., morepreferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours,more preferably 0.5 to 20 hours.

The polymer-bound acid generator should preferably have a weight averagemolecular weight (Mw) in the range of 1,000 to 500,000, and morepreferably 2,000 to 30,000, as measured by GPC versus polystyrenestandards using THF solvent. A Mw in the range ensures that the resistcomposition is heat resistant.

If a base polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the polymer-bound acid generator shouldpreferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially1.0 to 1.5, in order to provide a resist composition suitable formicropatterning to a small feature size.

It is understood that a blend of two or more polymer-bound acidgenerators which differ in compositional ratio. Mw or Mw/Mn isacceptable.

Other Components

With the polymer-bound acid generator defined above, other componentssuch as another acid generator, an organic solvent, surfactant,dissolution inhibitor, crosslinker, and quencher may be blended in anydesired combination to formulate a chemically amplified positive ornegative resist composition. This positive or negative resistcomposition has a very high sensitivity in that the dissolution rate indeveloper of the base polymer in exposed areas is accelerated bycatalytic reaction. In addition, the resist film has a high dissolutioncontrast, resolution, exposure latitude, and process adaptability, andprovides a good pattern profile after exposure, and minimal proximitybias because of restrained acid diffusion. By virtue of theseadvantages, the composition is fully useful in commercial applicationand suited as a pattern-forming material for the fabrication of VLSIs.Particularly when a chemically amplified positive resist compositioncapable of utilizing acid catalyzed reaction is formulated, thecomposition has a higher sensitivity and is further improved in theproperties described above.

The resist composition may contain an acid generator other than thepolymer-bound acid generator as long as the benefits of the inventionare not compromised. The other acid generator is typically a compound(PAG) capable of generating an acid upon exposure to actinic ray orradiation. Although the PAG used herein may be any compound capable ofgenerating an acid upon exposure to high-energy radiation, thosecompounds capable of generating sulfonic acid, imide acid (imidic acid)or methide acid are preferred. Suitable PAGs include sulfonium salts,iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. Exemplary acid generators aredescribed in U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs[0122]-[0142]).

Also, a sulfonium salt having the formula (1-1) and a iodonium salthaving the formula (1-2) are advantageously used as the other acidgenerator.

In formulae (1-1) and (1-2), R¹⁰¹, R¹⁰², R¹⁰³, R¹⁰⁴ and R¹⁰⁵ are eachindependently a C₅-C₂₀ straight, branched or cyclic monovalenthydrocarbon group which may contain a heteroatom, any two of R¹⁰¹, R¹⁰²and R¹⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached.

The cation moiety in the sulfonium salt having formula (1-1) is asexemplified above for the cation moiety in recurring unit (a1). Thecation moiety in the iodonium salt having formula (1-2) is asexemplified above for the cation moiety in recurring unit (a2).

In formulae (1-1) and (1-2), X⁻ is an anion selected from the formulae(1A) to (1D).

In formula (1A), R^(fa) is fluorine or a C₁-C₄₀ straight, branched orcyclic monovalent hydrocarbon group which may contain a heteroatom.

Of the anions of formula (1A), a structure having formula (1A′) ispreferred.

In formula (1A′), R¹⁰⁶ is hydrogen or trifluoromethyl, preferablytrifluoromethyl. R¹⁰⁷ is a C₁-C₃₈ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitableheteroatoms include oxygen, nitrogen, sulfur and halogen, with oxygenbeing preferred. Of the monovalent hydrocarbon groups, those of 6 to 30carbon atoms are preferred because a high resolution is available infine pattern formation. Suitable monovalent hydrocarbon groups includemethyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl,pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl, 3-cyclohexenyl,heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl,1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl,tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl,dicyclohexylmethyl, icosanyl, allyl, benzyl, diphenylmethyl,tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl,acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl,2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and3-oxocyclohexyl. Also included are the foregoing groups in which atleast one hydrogen is replaced by a radical containing a heteroatom suchas oxygen, sulfur, nitrogen or halogen, or in which at least one carbonatom is substituted by a radical containing a heteroatom such as oxygen,sulfur or nitrogen, so that the group may contain a hydroxyl, cyano,carbonyl, ether, ester, sulfonic acid ester, carbonate, lactone ring,sultone ring, carboxylic acid anhydride or haloalkyl radical.

With respect to the synthesis of the sulfonium salt having an anion offormula (1A′), reference is made to JP-A 2007-145797, JP-A 2008-106045,JP-A 2009-007327, and JP-A 2009-258695. Also useful are the sulfoniumsalts described in JP-A 2010-215608, JP-A 2012-041320, JP-A 2012-106986,and JP-A 2012-153644.

Examples of the anion having formula (1A) are shown below, but notlimited thereto.

In formula (1B), R^(fb1) and R^(fb2) are each independently fluorine ora C₁-C₀₄ straight, branched or cyclic monovalent hydrocarbon group whichmay contain a heteroatom. Suitable monovalent hydrocarbon groups are asexemplified above for R¹⁰⁷. Preferably R^(fb1) and R^(fb2) each arefluorine or a straight C₁-C₄ fluorinated alkyl group. A pair of R^(fb1)and R^(fb2) may bond together to form a ring with the linkage(—CF₂—SO₂—N⁻—SO₂—CF₂—) to which they are attached, and preferably thepair is a fluorinated ethylene or fluorinated propylene group.

In formula (1C), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a C₁-C₄₀ straight, branched or cyclic monovalent hydrocarbongroup which may contain a heteroatom. Suitable monovalent hydrocarbongroups are as exemplified above for R¹⁰⁷. Preferably R^(fc1), R^(fc2)and R^(fc3) each are fluorine or a straight C₁-C₄ fluorinated alkylgroup. A pair of R^(fc1) and R^(fc2) may bond together to form a ringwith the linkage (—CF₂—SO₂—C⁻—SO₂—CF₂—) to which they are attached, andpreferably the pair is a fluorinated ethylene or fluorinated propylenegroup.

In formula (1D), R^(fd) is a C₁-C₄₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁷.

With respect to the synthesis of the sulfonium salt having an anion offormula (1D), reference is made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the anion having formula (1D) are shown below, but notlimited thereto.

The compound having the anion of formula (1D) has a sufficient acidstrength to cleave acid labile groups in the base polymer because it isfree of fluorine at α-position of sulfo group, but has twotrifluoromethyl groups at β-position. Thus the compound is a useful PAG.

A compound having the formula (2) is also a useful PAG.

In formula (2), R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ straight,branched or cyclic monovalent hydrocarbon group which may contain aheteroatom. R²⁰³ is a C₁-C₃₀ straight, branched or cyclic divalenthydrocarbon group which may contain a heteroatom. Any two of R²⁰¹, R²⁰²and R²⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached. L^(A) is a single bond, ether group or a C₁-C₂₀straight, branched or cyclic divalent hydrocarbon group which maycontain a heteroatom. X^(A), X^(B), X^(C) and X^(D) are eachindependently hydrogen, fluorine or trifluoromethyl, with the provisothat at least one of X^(A), X^(B), X^(C) and X^(D) is fluorine ortrifluoromethyl, and k is an integer of 0 to 3.

Suitable monovalent hydrocarbon groups include methyl, ethyl, propyl,isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, t-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, 2-ethylhexyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl,cyclohexylethyl, cyclohexylbutyl, norbornyl, oxanorbornyl,tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl, phenyl, naphthyl andanthracenyl. Also included are the foregoing groups in which at leastone hydrogen is replaced by a heteroatom such as oxygen, sulfur,nitrogen or halogen, or in which at least one carbon is replaced by aheteroatom such as oxygen, sulfur or nitrogen, so that the group maycontain a hydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonicacid ester bond, carbonate bond, lactone ring, sultone ring, carboxylicacid anhydride or haloalkyl radical.

Suitable divalent hydrocarbon groups include linear alkane diyl groupssuch as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl,pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl,nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl;saturated cyclic divalent hydrocarbon groups such as cyclopentanediyl,cyclohexanediyl, norbornanediyl, and adamantanediyl, and unsaturatedcyclic divalent hydrocarbon groups such as phenylene and naphthylene.Also included are the foregoing groups in which at least one hydrogenatom is replaced by an alkyl group such as methyl, ethyl, propyl,n-butyl or t-butyl, or in which at least one hydrogen atom is replacedby a radical containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or in which at least one carbon atom is replaced by a radicalcontaining a heteroatom such as oxygen, sulfur or nitrogen, so that thegroup may contain a hydroxyl, cyano, carbonyl, ether, ester, sulfonicacid ester, carbonate, lactone ring, sultone ring, carboxylic acidanhydride or haloalkyl radical. Suitable heteroatoms include oxygen,nitrogen, sulfur and halogen, with oxygen being preferred.

Of the PAGs having formula (2), those having formula (2′) are preferred.

In formula (2′), L^(A) is as defined above. R is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a C₁-C₂₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁷. Thesubscripts x and y each are an integer of 0 to 5, and z is an integer of0 to 4.

Examples of the PAG having formula (2) are shown below, but not limitedthereto. Herein R is as defined above.

Of the foregoing PAGs, those compounds having an anion of formula (1A′)or (1D) are especially preferred because of reduced acid diffusion andhigh solubility in resist solvent, and those compounds having an anionof formula (2′) are especially preferred because of minimized aciddiffusion.

Also sulfonium and iodonium salts of iodized benzoyloxy-containingfluorinated sulfonic acid having the formulae (3-1) and (3-2) are usefulas the other acid generator.

In formulae (3-1) and (3-2), R³¹ is hydrogen, hydroxyl, carboxyl, nitro,cyano, fluorine, chlorine, bromine, amino group, or a straight, branchedor cyclic, C₁-C₂₀ alkyl, C₁-C₂₀ alkoxy. C₂-C₂₀ alkoxycarbonyl, C₂-C₂acyloxy or C₁-C₄ alkylsulfonyloxy group, which may contain fluorine,chlorine, bromine, hydroxy, amino or alkoxy moiety, or —NR³⁷—C(O)—R³⁸ or—NR³⁷—C(O)—O—R³⁸ wherein R³⁷ is hydrogen, or a straight, branched orcyclic C₁-C₆ alkyl group which may contain halogen, hydroxy, alkoxy,acyl or acyloxy moiety, R³⁸ is a straight, branched or cyclic, C₁-C₁₆alkyl or C₂-C₁₆ alkenyl group, or C₆-C₁₂ aryl group, which may containhalogen, hydroxy, alkoxy, acyl or acyloxy moiety. X¹¹ is a single bondor a C₁-C₂ divalent linking group when r=1, or a C₁-C₂₀ tri- ortetravalent linking group when r=2 or 3, the linking group optionallycontaining an oxygen, sulfur or nitrogen atom. Rf¹⁴ to Rf¹⁴ are eachindependently hydrogen, fluorine or trifluoromethyl, at least one ofRf¹¹ to R¹⁴ being fluorine or trifluoromethyl, or Rf¹¹ and Rf¹², takentogether, may form a carbonyl group. R³², R³³, R³⁴, R³⁵ and R³⁶ are eachindependently a C₁-C₁₂ straight, branched or cyclic alkyl group, C₂-C₁₂straight, branched or cyclic alkenyl group, C₁-C₂ straight, branched orcyclic alkynyl group, C₁-C₂₀ aryl group, C₁-C₁₂ aralkyl group or C₁-C₁₂aryloxyalkyl group, in which at least one hydrogen (one or more or evenall hydrogen atoms) may be substituted by a hydroxy, carboxy, halogen,cyano, oxo, amide, nitro, sultone, sulfone or sulfonium salt-containingmoiety, or in which an ether, ester, carbonyl, carbonate or sulfonicacid ester moiety may intervene between carbon atoms, or R³² and R³³ maybond together to form a ring with the sulfur atom to which they areattached, r is an integer of 1 to 3, s is an integer of 1 to 5, and t isan integer of 0 to 3.

Further, sulfonium and iodonium salts of iodized phenoxy or iodized tophenylalkoxy-containing fluorinated sulfonic acid having the formulae(3-3) and (3-4) are useful as the other acid generator.

In formulae (3-3) and (3-4). R⁴¹ is each independently a hydroxyl.C₁-C₂₀ straight, branched or cyclic alkyl or alkoxy group. C₁-C₂₀straight, branched or cyclic acyl or acyloxy group, fluorine, chlorine,bromine, amino, or alkoxycarbonyl-substituted amino group. R⁴² is eachindependently a single bond or C₁-C₄ alkylene group. R⁴³ is a singlebond or C₁-C₂₀ divalent linking group when u=1, or a C₁-C₂₀ tri- ortetravalent linking group when u=2 or 3, the linking group optionallycontaining an oxygen, sulfur or nitrogen atom. Rf²¹ to Rf²⁴ are eachindependently hydrogen, fluorine or trifluoromethyl, at least one ofRf²¹ to Rf²⁴ being fluorine or trifluoromethyl, or Rf²¹ and Rf²², takentogether, may form a carbonyl group. R⁴⁴, R⁴⁵, R⁴⁶, R⁴⁷ and R⁴⁸ are eachindependently a C₁-C₁₂ straight, branched or cyclic alkyl group, C₂-C₁₂straight, branched or cyclic alkenyl group, C₆-C₂₀ aryl group or C₁-C₁₂aralkyl or aryloxyalkyl group, in which at least one hydrogen (one ormore or even all hydrogen atoms) may be substituted by a hydroxyl,carboxyl, halogen, cyano, oxo, amide, nitro, sultone, sulfone, orsulfonium salt-containing moiety, or in which an ether, ester, carbonyl,carbonate or sulfonic acid ester moiety may intervene in a carbon-carbonbond, or R⁴⁴ and R⁴⁵ may bond together to form a ring with the sulfuratom to which they are attached, u is an integer of 1 to 3, v is aninteger of 1 to 5, and w is an integer of 0 to 3.

The cation moiety in the sulfonium salt having formula (3-1) or (3-3) isas exemplified above for the cation moiety in recurring unit (a1). Thecation moiety in the iodonium salt having formula (3-2) or (3-4) is asexemplified above for the cation moiety in recurring unit (a2).

Examples of the anion moiety in the onion salts having formulae (3-1) to(3-4) are given below, but not limited thereto.

In the resist composition, the other acid generator is preferably usedin an amount of 0 to 200 parts, more preferably 0.1 to 100 parts byweight per 100 parts by weight of the base polymer.

In the case of positive resist compositions, inclusion of a dissolutioninhibitor may lead to an increased difference in dissolution ratebetween exposed and unexposed areas and a further improvement inresolution. In the case of negative resist compositions, a negativepattern may be formed by adding a crosslinker to reduce the dissolutionrate of exposed area.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880).Exemplary solvents include ketones such as cyclohexanone, cyclopentanoneand methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butylpropionate, and propylene glycol mono-t-butyl ether acetate; andlactones such as γ-butyrolactone, which may be used alone or inadmixture.

The organic solvent is preferably added in an amount of 100 to 10.000parts, and more preferably 200 to 8,000 parts by weight per 100 parts byweight of the base polymer.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165]-[0166]. Inclusion of a surfactant may improve or control thecoating characteristics of the resist composition. The surfactant ispreferably added in an amount of 0.0001 to 10 parts by weight per 100parts by weight of the base polymer.

The dissolution inhibitor which can be used herein is a compound havingat least two phenolic hydroxyl groups on the molecule, in which anaverage of from 0 to 100 mol % of all the hydrogen atoms on the phenolichydroxyl groups are replaced by acid labile groups or a compound havingat least one carboxyl group on the molecule, in which an average of 50to 100 mol % of all the hydrogen atoms on the carboxyl groups arereplaced by acid labile groups, both the compounds having a molecularweight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenolA, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylicacid, adamantanecarboxylic acid, and cholic acid derivatives in whichthe hydrogen atom on the hydroxyl or carboxyl group is replaced by anacid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A2008-122932, paragraphs [0155]-[0178]).

In the positive resist composition, the dissolution inhibitor ispreferably added in an amount of 0 to 50 parts, more preferably 5 to 40parts by weight per 100 parts by weight of the base polymer.

Suitable crosslinkers which can be used herein include epoxy compounds,melamine compounds, guanamine compounds, glycoluril compounds and ureacompounds having substituted thereon at least one group selected fromamong methylol alkoxymethyl and acyloxymethyl groups, isocyanatecompounds, azide compounds, and compounds having a double bond such asan alkenyl ether group. These compounds may be used as an additive orintroduced into a polymer side chain as a pendant. Hydroxy-containingcompounds may also be used as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compoundsinclude tris(2,3-epoxypropyl) isocyanurate, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether, andtriethylolethane triglycidyl ether. Examples of the melamine compoundinclude hexamethylol melamine, hexamethoxymethyl melamine, hexamethylolmelamine compounds having 1 to 6 methylol groups methoxymethylated andmixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexanediisocyanate. Suitable azide compounds include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and4,4′-oxybisazide. Examples of the alkenyl ether group-containingcompound include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, and trimethylol propane trivinyl ether.

In the negative resist composition, the crosslinker is preferably addedin an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weightper 100 parts by weight of the base polymer.

In the resist composition of the invention, a quencher may be blended.The quencher is typically selected from conventional basic compounds.Conventional basic compounds include primary, secondary, and tertiaryaliphatic amines, mixed amines, aromatic amines, heterocyclic amines,nitrogen-containing compounds with carboxyl group, nitrogen-containingcompounds with sulfonyl group, nitrogen-containing compounds withhydroxyl group, nitrogen-containing compounds with hydroxyphenyl group,alcoholic nitrogen-containing compounds, amide derivatives, imidederivatives, and carbamate derivatives. Also included are primary,secondary, and tertiary amine compounds, specifically amine compoundshaving a hydroxyl, ether, ester, lactone ring, cyano, or sulfonic acidester group as described in JP-A 2008-111103, paragraphs [0146]-[0164],and compounds having a carbamate group as described in JP 3790649.Addition of a basic compound may be effective for further suppressingthe diffusion rate of acid in the resist film or correcting the patternprofile.

Onium salts such as sulfonium salts, iodonium salts and ammonium saltsof sulfonic acids which are not fluorinated at α-position and similaronium salts of carboxylic acid may also be used as the quencher. Whilean α-fluorinated sulfonic acid, imide acid, and methide acid arenecessary to deprotect the acid labile group of carboxylic acid ester,an α-non-fluorinated sulfonic acid or a carboxylic acid is released bysalt exchange with an α-non-fluorinated onium salt. An α-non-fluorinatedsulfonic acid and a carboxylic acid function as a quencher because theydo not induce deprotection reaction.

Also a carboxylic acid onium salt having the formula (4) is useful asthe quencher.

R⁴⁰¹—CO₂ ⁻M_(A) ⁺  (4)

In formula (4), R⁴⁰¹ is a C₁-C₄₀ straight, branched or cyclic monovalenthydrocarbon group which may contain a heteroatom. M_(A) ⁺ is an oniumion such as a sulfonium, iodonium or ammonium ion.

Preferably the anion moiety in the carboxylic acid onium salt has theformula (5).

In formula (5), R⁴⁰² and R⁴⁰³ are each independently hydrogen, fluorineor trifluoromethyl. R⁴⁰⁴ is hydrogen, hydroxyl, a C₁-C₃₅ straight,branched or cyclic monovalent hydrocarbon group which may contain aheteroatom, or a substituted or unsubstituted C₁-C₃₀ aryl group.

Also useful are quenchers of polymer type as described in U.S. Pat. No.7,598,016 (JP-A 2008-239918). The polymeric quencher segregates at theresist surface after coating and thus enhances the rectangularity ofresist pattern. When a protective film is applied as is often the casein the immersion lithography, the polymeric quencher is also effectivefor preventing a film thickness loss of resist pattern or rounding ofpattern top.

The quencher is preferably added in an amount of 0 to 5 parts, morepreferably 0 to 4 parts by weight per 100 parts by weight of the basepolymer.

To the resist composition, a polymeric additive (or water repellencyimprover) may also be added for improving the water repellency onsurface of a resist film as spin coated. The water repellency improvermay be used in the topcoatless immersion lithography. Suitable waterrepellency improvers include polymers having a fluoroalkyl group andpolymers having a specific structure with a1,1,1,3,33-hexafluoro-2-propanol residue and are described in JP-A2007-297590 and JP-A 2008-111103, for example. The water repellencyimprover to be added to the resist composition should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEB,thus preventing any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the basepolymer.

Also, an acetylene alcohol may be blended in the resist composition.Suitable acetylene alcohols are described in JP-A 2008-122932,paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcoholblended is 0 to 5 parts by weight per 100 parts by weight of the basepolymer.

Process

The resist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, prebaking, exposure, optional PEB, and development. Ifnecessary, any additional steps may be added.

For example, the positive resist composition is first applied onto asubstrate on which an integrated circuit is to be formed (e.g., Si,SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating)or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO,CrON, MoSi₂, or SiO₂) by a suitable coating technique such as spincoating, roll coating, flow coating, dipping, spraying or doctorcoating. The coating is prebaked on a hotplate at a temperature of 60 to150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C. for 30seconds to 20 minutes. The resulting resist film is generally 0.01 to2.0 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, EUV, x-ray, soft x-ray, excimer laserlight, γ-ray or synchrotron radiation, directly or through a mask. Theexposure dose is preferably about 1 to 200 mJ/cm², more preferably about10 to 100 mJ/cm², or about 0.1 to 100 μC/cm², more preferably about 0.5to 50 μC/cm². The resist film is further baked (PEB) on a hotplate at 60to 150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C. for30 seconds to 20 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution for 3 seconds to 3 minutes, preferably 5seconds to 2 minutes by conventional techniques such as dip, puddle andspray techniques. A typical developer is a 0.1 to 10 wt %, preferably 2to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide(TPAH), or tetrabutylammonium hydroxide (TBAH). The resist film in theexposed area is dissolved in the developer whereas the resist film inthe unexposed area is not dissolved. In this way, the desired positivepattern is formed on the substrate. Inversely in the case of negativeresist, the exposed area of resist film is insolubilized and theunexposed area is dissolved in the developer. It is appreciated that theresist composition of the invention is best suited for micro-patterningusing such high-energy radiation as KrF and ArF excimer laser, EB, EUV,x-ray, soft x-ray, γ-ray and synchrotron radiation.

In an alternative embodiment, a negative pattern may be formed viaorganic solvent development using a positive resist compositioncomprising a base polymer having an acid labile group. The developerused herein is preferably selected from among 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate,butyl formate, isobutyl formate, pentyl formate, isopentyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate,benzyl acetate, methyl phenylacetate, benzyl formate, phenylethylformate, methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether,di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentylether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atomsinclude hexane, heptane, octane, nonane, decane, undecane, dodecane,methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable aromatic solvents includetoluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene andmesitylene. The solvents may be used alone or in admixture.

Rinsing is effective for minimizing the risks of resist pattern collapseand defect formation. However, rinsing is not essential. If rinsing isomitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermalflow, RELACS® or DSA process. A hole pattern is shrunk by coating ashrink agent thereto, and baking such that the shrink agent may undergocrosslinking at the resist surface as a result of the acid catalystdiffusing from the resist layer during bake, and the shrink agent mayattach to the sidewall of the hole pattern. The bake is preferably at atemperature of 70 to 180° C., more preferably 80 to 170° C., for a timeof 10 to 300 seconds. The extra shrink agent is stripped and the holepattern is shrunk.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight.

PAG Monomers 1 to 7 and Comparative PAG Monomer 1 used in SynthesisExamples are identified below.

Synthesis Example 1 Synthesis of Polymer 1

A 2-L flask was charged with 8.4 g of 1-methyl-1-cyclopentylmethacrylate, 3.6 g of 4-hydroxyphenyl methacrylate, 4.5 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 8.1 g ofPAG Monomer 1, and 40 g of THF as solvent. The reactor was cooled at−70° C. in nitrogen atmosphere, after which vacuum pumping and nitrogenblow were repeated three times. The reactor was warmed up to roomtemperature, whereupon 1.2 g of azobisisobutyronitrile (AIBN) aspolymerization initiator was added. The reactor was heated at 60° C.,whereupon reaction ran for 15 hours. The reaction solution was poured tointo 1 L of isopropyl alcohol for precipitation. The white solidprecipitate was collected by filtration and dried in vacuum at 60° C.,yielding Polymer 1 in white solid form. Polymer 1 was analyzed forcomposition by ¹³C- and ¹H-NMR and for Mw and Mw/Mn by GPC.

Synthesis Example 2

Synthesis of Polymer 2

Polymer 2 was obtained in white solid form by the same procedure as inSynthesis Example 1 aside from using 10.3 g of PAG Monomer 2 instead ofPAG Monomer 1. Polymer 2 was analyzed for composition by ¹³C- and ¹H-NMRand for Mw and Mw/Mn by GPC.

Synthesis Example 3 Synthesis of Polymer 3

Polymer 3 was obtained in white solid form by the same procedure as inSynthesis Example 1 aside from using 10.3 g of PAG Monomer 3 instead ofPAG Monomer 1. Polymer 3 was analyzed for composition by ¹³C- and ¹H-NMRand for Mw and Mw/Mn by GPC.

Synthesis Example 4

Synthesis of Polymer 4

Polymer 4 was obtained in white solid form by the same procedure as inSynthesis Example 1 aside from using 9.3 g of PAG Monomer 4 instead ofPAG Monomer 1. Polymer 4 was analyzed for composition by ¹³C- and ¹H-NMRand for Mw and Mw/Mn by GPC.

Synthesis Example 5

Synthesis of Polymer 5

A 2-L flask was charged with 8.4 g of 1-methyl-1-cyclopentylmethacrylate, 4.8 g of 4-hydroxystyrene, 9.1 g of PAG Monomer 5, and 40g of THF as solvent. The reactor was cooled at −70° C. in nitrogenatmosphere, after which vacuum pumping and nitrogen blow were repeatedthree times. The reactor was warmed up to room temperature, whereupon1.2 g of AIBN as polymerization initiator was added. The reactor washeated at 60° C., whereupon reaction ran for 15 hours. The reactionsolution was poured into 1 L of isopropyl alcohol for precipitation. Thewhite solid precipitate was collected by filtration and dried in vacuumat 60° C., yielding Polymer 5 in white solid form. Polymer 5 wasanalyzed for composition by ¹³C- and ¹H-NMR and for Mw and Mw/Mn by GPC.

Synthesis Example 6

Synthesis of Polymer 6

Polymer 6 was obtained in white solid form by the same procedure as inSynthesis Example 5 aside from using 7.1 g of PAG Monomer 6 instead ofPAG Monomer 5. Polymer 6 was analyzed for composition by ¹³C- and ¹H-NMRand for Mw and Mw/Mn by GPC.

Synthesis Example 7

Synthesis of Polymer 7

Polymer 7 was obtained in white solid form by the same procedure as inSynthesis Example 5 aside from using 9.2 g of PAG Monomer 7 instead ofPAG Monomer 5. Polymer 7 was analyzed for composition by ¹³C- and ¹H-NMRand for Mw and Mw/Mn by GPC.

Synthesis Example 8

Synthesis of Polymer 8

Polymer 8 was obtained in white solid form by the same procedure as inSynthesis Example 7 aside from using 13.5 g of 4-amyloxy-3-fluorostyreneinstead of 1-methyl-1-cyclopentyl methacaylate and using 3.0 g of4-hydroxystyrene. Polymer 8 was analyzed for composition by ¹³C- and¹H-NMR and for Mw and Mw/Mn by GPC.

Comparative Synthesis Example 1

Synthesis of Comparative Polymer 1

Comparative Polymer 1 was obtained in white solid form by the sameprocedure as in Synthesis Example 1 aside from using 7.6 g ofComparative PAG Monomer 1 instead of PAG Monomer 1. The polymer wasanalyzed for composition by ¹³C- and ¹H-NMR and for Mw and Mw/Mn by GPC.

Examples 1 to 11 and Comparative Example 1 1) Preparation of ResistComposition

Resist compositions were prepared by dissolving components in a solventin accordance with the recipe shown in Table 1, and filtering through afilter having a pore size of 0.2 μm. The solvent contained 100 ppm ofsurfactant FC-4430 (3M). The components in Table 1 are as identifiedbelow.

Organic Solvents:

PGMEA (propylene glycol monomethyl ether acetate)

CyH (cyclohexanone)

PGME (propylene glycol monomethyl ether)

DAA (diacetone alcohol)

Acid Generators: PAG 1 to PAG 3 of the Following Structural Formulae

Quenchers: Quenchers 1 and 2 of the Following Structural Formulae

2) EUV Lithography Test

Each of the resist compositions of Examples 1 to 11 and ComparativeExample 1 was spin coated on a silicon substrate having a 20-nm coatingof silicon-containing spin-on hard mask SHB-A940 (silicon content 43 wt%, Shin-Etsu Chemical Co., Ltd.) and prebaked on a hotplate at 105° C.for 60 seconds to form a resist film of 60 nm thick. Using an EUVscanner NXE3300 (ASML, NA 0.33, σ0.9/0.6, quadrupole illumination), theresist film was exposed to EUV through a mask bearing a hole pattern ata pitch 46 in (on-wafer size) and +20% bias. The resist film was baked(PEB) on a hotplate at the temperature shown in Table 1 and developed ina 2.38 wt % TMAH aqueous solution for 30 seconds to form a hole patternhaving a size of 23 nm.

The resist pattern was evaluated. The exposure dose that provides a holepattern having a size of 23 nm is reported as sensitivity. The size of50 holes was measured under CD-SEM (CG-5000, Hitachi High-TechnologiesCorp.), from which a size variation (3σ) was computed and reported asCDU.

The resist composition is shown in Table 1 together with the sensitivityand CDU of EUV lithography.

TABLE 1 Acid PEB Polymer generator Base Organic solvent temp.Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 1Polymer 1 — Quencher 1 PGMEA (400) 100 28 2.1 (100) (3.00) CyH (2,000)PGME (100) Example 2 Polymer 2 — Quencher 1 PGMEA (400) 100 26 2.4 (100)(3.00) CyH (2,000) PGME (100) Example 3 Polymer 3 — Quencher 1 PGMEA(2,000) 100 24 2.2 (100) (3.00) DAA (500) Example 4 Polymer 4 — Quencher1 PGMEA (2,000) 100 23 2.2 (100) (3.00) DAA (500) Example 5 Polymer 5 —Quencher 1 PGMEA (2,000) 100 21 2.2 (100) (3.00) DAA (500) Example 6Polymer 6 — Quencher 1 PGMEA (2,000) 100 20 2.3 (100) (3.00) DAA (500)Example 7 Polymer 7 — Quencher 1 PGMEA (2,000) 100 20 2.4 (100) (3.00)DAA (500) Example 8 Polymer 8 — Quencher 1 PGMEA (2,000) 100 26 2.0(100) (3.00) DAA (500) Example 9 Polymer 1 PAG 1 Quencher 2 PGMEA(2,000) 100 17 2.7 (100) (7.0) (3.00) DAA (500) Example 10 Polymer 1 PAG2 Quencher 2 PGMEA (2,000) 100 16 2.7 (100) (10.0) (3.00) DAA (500)Example 11 Polymer 1 PAG 3 Quencher 2 PGMEA (2,000) 100 15 2.6 (100)(10.0) (3.00) DAA (500) Comparative Comparative — Quencher 1 PGMEA (400)100 36 4.0 Example 1 Polymer 1 (3.00) CyH (2,000) (100) PGME (100)

It is demonstrated in Table 1 that resist compositions comprising apolymer comprising recurring units of formula (a1) or (a2) within thescope of the invention offer a high sensitivity and improved CDU.

Japanese Patent Application No. 2017-100594 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A resist composition comprising a polymer comprising recurring unitshaving the formula (a1) or (a2):

wherein R^(A) is hydrogen or methyl, X¹ is a single bond or ester group,X² is a C₁-C₁₂ straight, branched or cyclic alkylene group or C₆-C₁₀arylene group, any methylene moiety in the alkylene group may besubstituted by an ether moiety, ester moiety or lactone ring-containingmoiety, at least one hydrogen in the group X² is substituted by iodine,X³ is a single bond, ether group, ester group or C₁-C₁₂ straight,branched or cyclic alkylene group, any methylene moiety in the alkylenegroup may be substituted by an ether or ester moiety, Rf¹ to Rf⁴ areeach independently hydrogen, fluorine or trifluoromethyl, at least oneof Rf¹ to Rf⁴ is fluorine or trifluoromethyl, Rf¹ and Rf² may bondtogether to form a carbonyl group, R¹ to R⁵ are each independently aC₁-C₁₂ straight, branched or cyclic alkyl group, C₂-C₁₂ straight,branched or cyclic alkenyl group, C₂-C₁₂ straight, branched or cyclicalkynyl group, C₆-C₂₀ aryl group, C₇-C₁₂ aralkyl group, or C₇-C₁₂aryloxyalkyl group, in which at least one hydrogen may be substituted byhydroxyl, carboxyl, halogen, oxo, cyano, amide, nitro, sultone, sulfoneor sulfonium salt-containing moiety, and in which any methylene moietymay be substituted by an ether, ester, carbonyl, carbonate or sulfonatemoiety, and R¹ and R² may bond together to form a ring with the sulfuratom to which they are attached.
 2. The resist composition of claim 1wherein the recurring units having formulae (a1) and (a2) arerepresented by the formulae (a1-1) and (a2-1), respectively,

wherein R^(A), R¹ to R⁵, Rf¹ to Rf⁴, and X¹ are as defined above, R⁶ isa C₁-C₄ straight, branched or cyclic alkyl group, halogen atom exclusiveof iodine, hydroxyl group, C₁-C₄ straight, branched or cyclic alkoxygroup, or C₂-C₅ straight, branched or cyclic alkoxycarbonyl group, m isan integer of 1 to 4, and n is an integer of 0 to
 3. 3. The resistcomposition of claim 1, further comprising an organic solvent.
 4. Theresist composition of claim 1, wherein the polymer further comprisesrecurring units having the formula (b1) or (b2):

wherein R^(A) is independently hydrogen or methyl, Y¹ is a single bond,phenylene group, naphthylene group, or a C₁-C₁₂ linking group containingan ester moiety and/or lactone ring, Y² is a single bond or ester group,R¹¹ and R¹² are each independently an acid labile group, R¹³ is halogen,trifluoromethyl, cyano, C₁-C₆ straight, branched or cyclic alkyl oralkoxy group, or C₂-C₇ straight, branched or cyclic acyl, acyloxy oralkoxycarbonyl group, R¹⁴ is a single bond or C₁-C₆ straight or branchedalkylene group in which at least one carbon atom may be substituted byan ether or ester moiety, p is 1 or 2, and q is an integer of 0 to
 4. 5.The resist composition of claim 4, further comprising a dissolutioninhibitor, the resist composition being a chemically amplified positivetone resist composition.
 6. The resist composition of claim 1 whereinthe polymer is free of an acid labile group.
 7. The resist compositionof claim 6, further comprising a crosslinker, the resist compositionbeing a chemically amplified negative tone resist composition.
 8. Theresist composition of claim 1, further comprising a surfactant.
 9. Aprocess for forming a pattern comprising the steps of applying theresist composition of claim 1 onto a substrate, baking to form a resistfilm, exposing the resist film to high-energy radiation, and developingthe exposed film in a developer.
 10. The process of claim 9 wherein thehigh-energy radiation is ArF excimer laser radiation of wavelength 193nm or KrF excimer laser radiation of wavelength 248 nm.
 11. The processof claim 9 wherein the high-energy radiation is electron beam or extremeultraviolet radiation of wavelength 3 to 15 nm.